Evolution refers to the changes over time experienced by living things, associated with genomic variation. The genetic material embodied by DNA transcends organisms in a few ways.
One of them is vertical inheritance from parents to offspring via asexual or sexual reproduction. Another path is horizontal transmission between unrelated individuals, as seen between bacteria that exchange antibiotic resistance genes through the sharing of their plasmids.
Genetic variation in bacteria in the context of evolution of antibiotic resistance is a good case study.
(1) Genetic – why? All of the characteristics of bacterial organisms are a result of the blueprint for the various proteins coded in their DNA, the same DNA that all life has on Earth (except for the specific base sequence). Genetic simply means arising from DNA.
(2) Variation – bacteria have variation? Who would have thought? I mean, I always thought they were just a bunch of tiny hot dogs without the sausage in the middle, hanging around causing trouble. Well, I found out, no, they’re not hot dogs. They’re beautiful organisms in their own right, and if it wasn’t for our inherent bias of being on the receiving end of their infection, they wouldn’t be baddies. They could be heroes. In fact, some of them are heroes! Some bacteria do contribute positively to our life. The undeniable evidence for that is pickles.